The Intelligent Network (IN) and associated Universal Personal Telecommunication (UPT), and Personal Communication Network (PCN) services are becoming more important as the amount of mobile communications and other similar telecommunication services increase. In a proposed PCN, for example, a wired information network and a wireless network will be maintained. A PCN would allow a large number of mobile customers to initiate and receive calls while moving from one location to another. Customer positions would be tracked and their location information maintained in network databases.
A proposed method to support terminal mobility requires a home database (or Home Location Register, HLR) and a visitor database (or Visitor Location Register, VLR). In a proposed design, the home database is accessed by a fixed, wired network while the visitor database is connected to a switch in the wireless network. The routing and other signaling functions of each call initiated from or destined for mobile customers requires a use of the information stored in the databases.
Universal Personal Telecommunication services allow personal mobility. In essence, each user can initiate and receive calls by using a unique personal telephone number (referred to as a Personal Telecommunication Number, PTN) on any fixed or mobile terminal no matter the geographical location of the user. As a result, calls destined for a particular PTN can be routed to its customer's home, office, car, or answering service according to the routing plan specified by the customer. Again, the extensive use of signaling databases, i.e., network databases, for call routing and other signaling functions is required.
As these services become more popular and the traffic load associated with these services grow, the number of queries and updates (corresponding to one customer record) to the databases will also increase dramatically. As a result, it will be advantageous to distribute and replicate customer records in multiple geographical locations, i.e., sites, of the signaling network for easy access, achieving a high level of efficiency and system availability as well as an improved call setup time.
Typically, the drawback of data distribution and replication is the overhead incurred by the concurrency control protocols to maintain the correctness and consistency of records stored at various sites. To allow recovery after system failure at different sites, a set of commitment protocols becomes necessary. These commitment protocols not only complicate the system design, but also add more overhead to the system operations. Thus, there is a trade off between the performance gained by data distribution and replication, and loss of efficiency resulting from overhead.
Some high security computer database systems, such as used by banks, require stringent protocol, e.g., Primary-Site Locking (PSL), or when lower security is possible, Basic Time-Stamp (BTS) protocol. A Primary-Site Locking system would be necessary in a bank database computer system where any secondary database would have to be locked until all data is updated and verified as accurate. Otherwise, withdrawals could be made spontaneously from two different geographic locations even though one withdrawal would delete the account and the second transaction would withdraw funds when the account actually had no existing funds. To prevent such occurrences, secondary databases are locked until updated so that no withdrawals can occur. This could dramatically slow down banking time.
In telecommunications, however, inconsistency between replicated copies of customer records for a brief period of time can be tolerated because the major consequence of accessing obsolete information will be a "call misroute". The network can allow a small fraction of calls misrouted as long as the number of misrouted calls is very small compared to the overall call volume.